[modern] Heater Problem

Disused Categories Modern
1

Hi All,

I have just become the proud owner of an '89 Jag Sovereign 3.6.
One problem I have is that the heater fan will only run on high speed. I’ve
had the console out and checked the switch contacts, these are all working
correctly. According to the Haynes manual, the wiring goes back to a
microprocessor somewhere.
Has anyone had a similar problem. I suspect that the problem may be the
computer control unit, but I don’t know where Jaguar have hidden it. I can
hear the vents moving when I change the temperature and warm air comes out
when travelling at a reasonable speed. Also, I can’t get any air from the
vents in the centre of the dashboard.

Can anyone suggest a coarse of action.

John
89 XJ40 Sov.

2

Hello John
Your heater problem is almost certainly the speed control electronics inside
the two blower motor casings under the dash. I’ve just finished the same job
on my '88 Sov. There are many postings on the subject in the list archives;
those & the Jag Lovers XJ40 manual are most likely your best starting point.
I (& others with probably greater experience!) will be glad to help where
possible. I also have some spare electronic components for the job if you
need them & have difficulty finding them elsewhere. I guess you’re UK
based - whereabouts?
Re the centre vents, are you aware that they only open when the coldest
setting is selected?
All the best
John
(Suffolk, UK)
'88 Sov 230k----- Original Message -----
From: John Parkin jmparkin@blueyonder.co.uk
To: Jag-Lovers (E-mail) modern@jag-lovers.org
Sent: Thursday, March 15, 2001 10:33 PM
Subject: [modern] Heater Problem

Hi All,

I have just become the proud owner of an '89 Jag Sovereign 3.6.
One problem I have is that the heater fan will only run on high speed.
I’ve
had the console out and checked the switch contacts, these are all working
correctly. According to the Haynes manual, the wiring goes back to a
microprocessor somewhere.
Has anyone had a similar problem. I suspect that the problem may be the
computer control unit, but I don’t know where Jaguar have hidden it. I can
hear the vents moving when I change the temperature and warm air comes out
when travelling at a reasonable speed. Also, I can’t get any air from the
vents in the centre of the dashboard.

Can anyone suggest a coarse of action.

John
89 XJ40 Sov.

3

John,
You need to remove both blowers and service them.
They have relay or speed control transistors inside
that are blown out.

The motors are the open type, and get exposed to any dirt
that gets in the air intake.
The dirt and age causes the motors to bind up, and blow
the speed control circuitry.

Easy to get them apart, clean and lube the motors,
check the brushes(pull springs apart) and replace the speed
control transistor.
details on the web page, and the transistor costs
about $4.50 in the U.S.

It sounds like the rest of the system is working ok,
the ECU is on the right side of the system, and does not typically
cause problems unless water gets into it from clogged drains.

Its very common for everyone to blame ECU’s on all cars,
but they very rarely cause any problem on most cars,
including the Jaguar.

On the Jaguar, its dirty micro switches, bad solder joints,
dirty connections, worn out bits, water getting into
things…

Brett
1990 XJ6> -----Original Message-----

From: owner-modern@jag-lovers.org [mailto:owner-modern@jag-lovers.org]On
Behalf Of John Parkin
Sent: Thursday, March 15, 2001 5:33 PM
To: Jag-Lovers (E-mail)
Subject: [modern] Heater Problem

Hi All,

I have just become the proud owner of an '89 Jag Sovereign 3.6.
One problem I have is that the heater fan will only run on high
speed. I’ve
had the console out and checked the switch contacts, these are all working
correctly. According to the Haynes manual, the wiring goes back to a
microprocessor somewhere.
Has anyone had a similar problem. I suspect that the problem may be the
computer control unit, but I don’t know where Jaguar have hidden it. I can
hear the vents moving when I change the temperature and warm air comes out
when travelling at a reasonable speed. Also, I can’t get any air from the
vents in the centre of the dashboard.

Can anyone suggest a coarse of action.

John
89 XJ40 Sov.